[Drawkit] zoom to bounding box

[Graham Cox]

On 03/04/2009, at 12:16 PM, Michael Caron wrote:

> Hi Graham,
>
> I've been looking through the DrawKit code to figure out how to zoom  
> to a bounding box, or perhaps crop the drawing to the bounding box  
> of the drawable objects.
>
> There's the DKDrawableObject class method,
>
> + (NSRect) unionOfBoundsOfDrawablesInArray:(NSArray*) array;
>
> and the scrollToRect:(NSRect)r method on DKDrawing, but I haven't  
> found anything that would zoom to a box. Glad to add it, but being  
> new to the framework I don't want to do something that's already  
> done in a different way.
>
> For a use case, consider a bounding box on a group of objects with  
> top left corner at (110, 130) and bottom right corner at (300, 390).  
> so everything to the left of 110 on the x-axis and everything above  
> 130 on the y axis (in a flipped coordinate system), is blank. I'd  
> like to zoom to the bounding box so that the drawing itself is not  
> resized, but the scale is set appropriately so the object collection  
> is nicely centered in the view.
>
> Any tips?
>


Michael,

It sounds like what you want is the -zoomViewToRect: method  
implemented by GCZoomView and inherited by DKDrawingView. This only  
affects the way the drawing is presented - it doesn't alter anything  
about the content of the drawing, so it's not a permanent crop, for  
example.

To determine the rect bounding all possible drawables, you'll need to  
examine each layer that contains drawables and find their bounds using  
-unionOfAllObjectBounds (see DKObjectOwnerLayer), then union the  
results from all layers. The method you mention is really a general  
utility method which in this case would be slightly harder to use than  
just asking each layer to tell you the bounds of its objects.

--Graham